1. Field of the Invention
The present invention relates to a method of shaping a sheet of glass with a suction mold.
2. Description of the Prior Art
There has heretofore been known a method of bending a sheet of glass by drawing, under suction, the sheet of glass that has been heated nearly to a softening point thereof against the surface of a suction mold for thereby shaping the sheet of glass complementarily to the surface configuration of the suction mold. Such a method is disclosed in Japanese laid-open patent publication No. 62-270429 and Japanese patent publication No. 62-30136.
According to the method disclosed in the former publication, a heated sheet of glass is floated by air and pressed against the shaping surface of a suction mold, and then a vacuum is developed by the suction mold to draw the heated sheet of glass against the shaping surface of the suction mold to bend the heated sheet of glass to a desired shape complementary to the shaping surface.
According to the method disclosed in the latter publication, a heated sheet of glass is lifted by a ring mold and pressed against the shaping surface of a suction mold, and then a vacuum is developed by the suction mold to draw the heated sheet of glass against the shaping surface of the suction mold to bend the heated sheet of glass to a desired shape complementary to the shaping surface.
In the above prior arrangements, a large amount of air may flow into the suction mold through suction holes that are defined in the region of the suction mold which is positioned out of intimate contact with the glass sheet, thereby reducing the forces with which the glass sheet is held against the shaping surface under suction.
To solve the above problem, a suction mold is divided into a plurality of chambers, and different suction pressures are developed in the respective chambers according to other conventional arrangements disclosed in Japanese laid-open utility model publication No. 63-27443 and Japanese laid-open patent publication No. 59-232926. These disclosed suction molds also suffer disadvantages because suction pressures are simultaneously developed in the chambers.
More specifically, FIG. 8A the accompanying drawings shows a conventional suction mold 100 having a downwardly convex shaping surface. In FIG. 8A, a heated glass sheet G has its peripheral edge pressed against the peripheral edge of the shaping surface of the suction mold 100 by a ring mold 101. When the suction mold 100 starts drawing the heated glass sheet G under suction pressures developed therein, air may locally be not removed from and may remain trapped between the glass sheet G and the shaping surface of the suction mold 100, as shown in FIG. 8B of the accompanying drawings. When this happens, the glass sheet G has an inversely curved region which will cause poor reflective distortions on the bent glass sheet.
FIG. 9A of the accompanying drawings shows another conventional suction mold 110 of the reversal type having a concave/convex shaping surface. In FIG. 9A, a heated glass sheet G has its peripheral edge pressed against the peripheral edge of the shaping surface of the suction mold 110. When the suction mold 110 starts drawing the heated glass sheet G under suction pressures developed therein, the heated glass sheet G may not be stretched sufficiently, and may be ruptured as shown in FIG. 9B of the accompanying drawings.
It is therefore an object of the present invention to provide a method of shaping a sheet of glass accurately to a desired shape with a suction mold, without trapping air between the sheet of glass and the shaping surface of the suction mold, or rupturing the sheet of glass or developing undue stresses in the sheet of glass.
According to the present invention, there is provided a method of shaping a sheet of glass heated nearly to a softening point thereof with the shaping surface areas of a plurality of divided suction chambers defined in a suction mold, the shaping surface areas having suction holes defined therein, comprising the steps of introducing a vacuum into one of the suction chambers to attract an area of the sheet of glass against the shaping surface area of the one of the suction chambers through the suction holes thereof, and thereafter, introducing a vacuum into another of the suction chambers to attract another area of the sheet of glass against the shaping surface area of the other of the suction chambers through the suction holes thereof.
The above and further objects, details and advantages of the present invention will become apparent from the following detailed description of preferred embodiments thereof, when read in conjunction with the accompanying drawings.